This invention pertains to a sample sweeping and injection device for use in liquid-phase chromatography apparatus.
A liquid-phase chromatography apparatus comprises the following components, in the direction of flow:
(1) A RESERVOIR FOR CARRIER LIQUID;
(2) A CARRIER LIQUID PUMPING SYSTEM, TO MOVE SAID CARRIER LIQUID TOWARD THE SEPARATION COLUMN;
(3) A HEAD FOR INJECTING THE CARRIER LIQUID INTO THE SEPARATION COLUMN;
(4) A SYSTEM FOR INJECTING THE SAMPLE TO BE ANALYZED;
(5) A SEPARATION COLUMN WHEREIN THE ANALYSIS TAKES PLACE, THAT IS, WHERE THE SAMPLE IS SEPARATED INTO ITS VARIOUS CONSTITUENTS; THIS COLUMN IS FILLED WITH A PACKING OR SUBSTRATE;
(6) A DETECTOR OF A TYPE DEPENDING UPON THE NATURE OF THE MOLECULES TO BE DEVELOPED.
The functioning of the separation column of a liquid-phase chromatography apparatus may be affected by the geometry of the various components of the injection system-separation column assembly, more specifically by the presence of dead volumes and particularly by the precision with which the sample to be analyzed is injected at the head of the column, since the carrier liquid must percolate through the column at a slow, constant rate.
In high-performance liquid-phase chromatography, the samples to be analyzed are injected either by means of a syringe which pierces a partition or by means of a rotary valve or a slide valve. Volumes ranging from 1 microliter to more than 200 microliters can be injected, depending on the type of valve. These two means of injection both present drawbacks.
First, the conditions of injection with a syringe are difficult to reproduce from one analysis to the next and, second, the sample is often injected at a linear speed higher than the linear speed of the carrier liquid, thus giving rise to turbulence at the entrance to the separation column.
Valves can be used for quantitative analysis, because they yield a higher degree of reproducibility of injection conditions; nevertheless, their design causes the efficiency of separation to be reduced by one-half to as much as two-thirds of the number of theoretical bands attainable with ideal injections using syringes.
Thus, it is not unusual to obtain an efficiency of 8,000 theoretical bands using a syringe and a separation column 10 centimeters in length and 4 millimeters in inside diameter, while the same column may have an efficiency of no more than 3,000-4,000 theoretical bands when injected by means of a rotary or slide valve.
In an attempt to bring together the advantages of the syringe and valve modes of operation, it has been proposed to inject the sample by means of a loop injection valve centered on the end of the separation column and to feed the carrier liquid annularly all around the point of injection of the sample. To this end, a suitable injection chamber has been proposed, containing a sample injection tube and an annular chamber for distributing the carrier liquid around the injection tube at the head of the separation column. The carrier liquid is fed toward the injection chamber by means of a "T" coupling which distributes the carrier liquid to the annular distribution chamber through a capillary tube and to the sample loop injection valve through an all-or-nothing valve.
This mode of injection still presents drawbacks, however. In fact, before the sample is injected, all the carrier liquid drains toward the column through the capillary tube, with a great loss of head; at the moment the sample is injected, the greater part of the flow of the carrier liquid is directed toward the loop injection valve, causing the loss of head of the carrier liquid flow to change abruptly. This variation results in a variation in the flow of carrier liquid sweeping the separation column. This head loss variation consequently alters the rate of flow of the carrier liquid inside the separation column and consequently disturbs the analysis of the sample.